Electrical dental furnace.



PATENTED FEB. 7, 1905.

L. L. BOSWORTH. ELECTRICAL DENTAL FURNACE.

APPLICATION FILED MAB. 6, 1904.

2 SHEETS-SHEET 1.

' 1N VENTOR.

ATTORNEY.

WIHVESSES:

PATENTED FEB. 7, 1905.

L. L. .BOSWORTH.

ELECTRICAL DENTAL FURNACE.

APPLICATION FILED MAR. 5, 1904.

2 SHEETS-SHEET 2.

WITNESSES:

IN VEN TOR. M4. mmwra A TTORNE Y.

LUTHER L. BOSIVORTH, OF CLEVELAND,

Patented February '7, 1905.

ATENT Orricn.

OHIO.

ELECTRICAL DENTAL FURNAQE.

SPECIFICATION forming part of Letters PatentNo. 781,762, dated February '7', 1905.

Application filed March 5,1904. Serial No. 196,767.

Ohio, have invented certain new and useful Improvements in Electrical Dental Furnaces; and I do declare that the following 'is a full, clear, and exact description of the invention, which will enable others skilled in the art to which it appertains to make and use the same.

My invention relates to electrical dental furnaces; and the invention consists in a furnace constructed and adapted to operate substantially as shown and described, and particularly pointed out in the claims.

In the accompanying drawings, Figure 1 is a perspective view of the furnace complete and assembled for use. Fig. 2 is a perspective view of the earthen body and its casing and with the end B and the muffle members F and G removed. Fig. 3 is a perspective view of the outer mufiie member or section, and Fig. 4c is a perspective view of the inner muflie member or section. Fig. 5 is an enlarged longitudinal sectional elevation of the furnace with its parts assembled as in Fig. 1; and Fig. 6 is a cross-section thereof on line a a, Fig. 5.

In the development of the furnace as thus shown I have had especially in mind a construction which will reduce the operating expense to the minimum and make the furnace easy to repair when it burns out or is otherwise damaged in use.

Hitherto in dental furnaces with have come under my observation and are in more or less general use among dentists there has been very great annoyance and expense attending the operation of the same because the heatingwire is embedded in the muffle, and hence repair of the wire is impossible. Nothing but a new muffle will do, and this is expensive as an article and annoying to obtain because it has to be gotten from the factory and often involves weeks of delay. By my improved construction I provide a separable muffle with the platinum wire exposed, so that it can be easily repaired and the user of this furnace can himself make such repairs without any material delay. My experiencehas been that owing to the very intense heat in a furnace of this kind the platinum wire cannot endure more than comparatively few minutes before it burns out at some point, andI claim no immunity for the wire by my construction; but what I do claim is a construction which enables a dentist or other user of the furnace to make the repairs on the spot and inexpensively, and resume the use of the furnace in a Very brief time after a burn-out has occurred.

Referring to the drawings, the invention is embodied in a casing or shell comprising a cylindrical body A and two ends B B, secured upon the said body in any suitable way, and provided with legs Z), which serve as supports. Usually end B is removable and end B may be also, but not necessarily.

O is a fire-clay or like refractory body inclosed within the shell or casing and constituting a support for a resistance-coil about the same, as well as providing a muffle-receiving cavity 0 in one end, which is also referred to herein as an oven. The said body O is preferably made up as a separate article of man ufacture for my use, and may be constituted of lire-clay or any other suitable material which has firmness enough to hold its shape and is reasonably light in weight. I do not, therefore, limit myself to lire-clay for this purpose, nor to the manner of providing said body, as I can build it into its windings from plastic material which will harden for use. The said body is a part of somewhat less crosssection than the interiorof the casing and has two convolutions or windings of resistancewire I) spirally around the same from end to end, the inner convolution or winding being directly upon the said body itself and the outer winding upon or about an asbestos or equivalentnon-conducting covering or jacket 0, fitting closely about body G. Then there is a wall 0 of asbestos or the like interposed between body O and the metallic shell without, so that said parts are completely insulated from each other electrically.

The terminals 2 and I of the resistance coils or wire Dare at the front end of the furnace, and current-conductors 5 and 6, such as wires or the like, extend through head B at the rear and body O and are provided with bindingposts or the like at their rear ends to connect the line-wires. At their opposite or front ends connections are made between conductor 5 and terminal 2 of the resistance-wire, and further connection is made between conductor 6 and terminal 4 by interposed muflie-heating platinum coil or winding H. Thus end 7/. of winding H is detachably connected with conductor 6 and it with terminal i, thereby completing the line-circuit. The current enters through conductor 5 and leaves by conductor 6.

It has been observed that refractory body C is provided with an oven and said oven is substantially triangular in cross-section, with one side forming the bottom of the oven and the other two sides the convergingwalls and roof thereof, and the said oven tapers gradually inward to produce a substantially conical opening smallest at its rear.

The muiile consists of two sections F and G, which are adapted to occupy cavity or oven 0, and these are telescoped or sleeved one upon or over the other that is, the outer or inclosing section F wholly envelops and incloses the inner one about its side and extremity and constitutes a wall just within the wall of the oven for the inner section, but is removable with section G. Hence in a practical sense said outer section constitutes a protecting and working jacket for the inner one, and by usinga double and separable muffle 1 am enabled to get all the advantage of a single muffle with the heating-wire embedded therein, but obtain the added and very natural advantage of having the wire within reach when it burns out and should be repairable. In such case the inner muffle-section is simply withdrawn from the outer one and the broken Wire is openly exposed and can be quickly mended. Head B of the casing has a triangular hole 6 formed centrally therein directly in front of the oven and corresponding thereto, but of a size approaching more nearly to the internal dimensions of the inner nmflie-section, so that when the mufile is deposited in the oven and the front plate or head B is put in place it serves to confine the muflie in working position. A hearth-plate Z)" is secured upon head B in front of the oven at the lower edge of opening 6 and an isinglass or other closure is employed to temporarily close the oven and confine the heat.

The two muiiie-sections F and G are pref erably made of Hessian sand or other refractory material of very high heat resistance and which is firm and strong in service, and asbestos or equivalent non-heat-eonveying lining 9 is interposed between outer section F and the wall of the oven. The inner muflle or muffle-section G is tightly wound with a preferably platinum heating-wire H and the inner end /i thereof is wrapped across the end of said section and passed through a hole in the rear portion of the outer section, Fig. 3, whence it is carried forward from the back of said section for convenient connection with one of the terminals or current connections of the resistance-coil about body C. The other end, it, -of wire H is connected with the other terminal of the resistance-coil, and both connections are thus broughtconveniently just inside the head B. The said head or plate is removably secu red in place by any convenient means and is shown as having a rim or flange 7) sleeved upon shell or cylinder A, and screws or other means may be used to make the engagement temporarily effective. The mufiie-sections can be removed separately or together, and in the case the platinum heating-wire gets burned out by overheating the furnace or from other cause repair of the wire can be made at once and the use of the furnace resumed by simply connecting up the broken ends by a suitable insertion.

By reason of the shape of the muffle the ten'iperature of the furnace gradually increases from front to rear, and a higher temperature is obtained at the rear or smaller end than at the front, although the temperature of the heating wire is the same throughout its length. and hence this furnace can be placed in an inclined or perpemlicular position and used by jewelers as a crucible for fusing precious metals, as well as for other purposes requiring high temperature within a limited compass.

The outer section of the muffle is necessarily of such high heat resistance that it will not fuse at any of the very high temperatures to which a furnace of this kind is subjected and to this end needs to have at least the quality and endurance of the inner section. Experience has shown me that ordinary fire-clay will not suffice, because it fuses at a comparatively low temperature, as does also asbestos; but sections or parts made of Hessian sand will stand the highest pressure and heat met with in these furnaces without being at all affected thereby. This also avoids the injury to the platinum wire which any fused jacket or covering will produce, because when fusing of the covering occurs the wire is affected thereby, and particles adhere thereto and so embed it that it cannot be mended when burned out. This 1 wholly avoid by an outer mufiic-section, which protects the wire in the particulars just mentioned.

\Vhat I claim is- 1. in electrical dental furnaces, a two-part separable mufiic having one part telescoped within the other and a heating-coil covered in between said parts, substantially as described.

2. in electrical dental furnaces, a tapered muffle consisting of two sections telescopically and separably united and a heatingwire wound about the inner section and covered by the outer section, substantially as described.

3. An electrical dental furnace comprising a mu file of tapered form smallest at its closed. inner end and consisting of an electricallywound inner section and an unwound outer section fitting closely upon the inner section, said inner section having the Winding removable therewith and exposed on the surface thereof for repairs, substantially as described.

4:. In electrical dental furnaces, a sectional muiiie consisting of a plain outer section and an electrically Wound inner section nested Within the outer section, and a non-conducting body having a cavity containing said muflie, substantially as described.

5. In dental furnaces, a body of anon-conducting material having a cavity in its end and a resistance-coil about said body, in combination With a separable two-part mufi'le occupying said cavity and an electrical Winding about the inner part of the mufi'le connected with the said resistance-coil, substantially as de scribed.

6. A dental furnace comprising a suitable casing, a body of non-conducting material therein having a cavity in one end and a resistance-wire Wound about said body, in combination with a sectional muflie fitting said cavity, the outer section thereof being plain and the inner section Wired about its outside and connected up with said resistance-coil, and conductors for the electric current extending to the opposite end of said body, substantially as described.

7. In electrical furnaces, a suitable casing and a non-conducting body therein and insulated therefrom, a resistance-coil about said body and conductors for the current extending through the same from end to end, in combination with a mufiic consisting of telescopically-united sections inclosed in a cavity in said body and a heating-Wire between said sections having one end connected with one of the terminals of the said resistance-coil and the other end With one of said conductors, the inner end of said Wire extending through the Wall of the outer mulile-section, substantially as described.

In testimony whereof I sign this specification in the presence of two Witnesses.

LUTHER L. BOS\VORTH.

Witnesses:

R. B. Mosnn, C. A. SELL. 

